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<h1 id="firstHeading" class="firstHeading">动态异常说明</h1>
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                    <div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../../cpp.html" title="cpp"> C++</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
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<tr class="t-nv"><td colspan="5"> <a href="throw.html" title="cpp/language/throw">throw 表达式</a></td></tr>
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<p>列出函数可能直接或间接抛出的异常。
</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>throw(</b></code> <code><b>)</b></code>
</td>
<td> (1)
</td>
<td> <span class="t-mark-rev t-deprecated-cxx11">(C++11 中弃用)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>throw(</b></code><span class="t-spar">类型标识, 类型标识, ...</span><code><b>)</b></code>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-deprecated-cxx11">(C++11 中弃用)</span><span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
 <table class="t-rev-begin">
<tr class="t-rev t-until-cxx17"><td>
<div class="t-li1"><span class="t-li">1)</span> 不抛出动态异常说明
</div></td>
<td><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td></tr>
<tr class="t-rev t-since-cxx17"><td>
<div class="t-li1"><span class="t-li">1)</span> 与 <a href="noexcept_spec.html" title="cpp/language/noexcept spec"><tt>noexcept(true)</tt></a> 相同
</div></td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td></tr>
</table>
<div class="t-li1"><span class="t-li">2)</span> 显式动态异常说明</div>
<p>这种说明仅可出现在作为类型为函数类型、函数指针类型、函数引用类型、成员函数指针类型的函数、变量、非静态数据成员的声明符的，<span class="t-rev-inl t-until-cxx17"><span>顶层</span> <span><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></span></span> lambda 声明符或函数声明符上。它可以出现在形参的声明符或返回类型的声明符上。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK：函数声明</span>
<span class="kw4">void</span> <span class="br0">(</span><span class="sy2">*</span>pf<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span> <span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK：函数指针声明</span>
<span class="kw4">void</span> g<span class="br0">(</span><span class="kw4">void</span> pfa<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK：函数指针形参声明</span>
<span class="kw1">typedef</span> <span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>pf<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 错误：typedef 声明</span></pre></div></div>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<p>若某个函数的声明将类型 <code>T</code> 列于其异常说明，则该函数可以抛出该类型或从该类型派生的类型的异常。
</p><p>异常说明中不允许出现<a href="incomplete_type.html#.E4.B8.8D.E5.AE.8C.E6.95.B4.E7.B1.BB.E5.9E.8B" title="cpp/language/type">不完整类型</a>，除 cv <code>void*</code> 之外的到不完整类型的指针或引用，以及右值引用类型。若使用数组和函数类型，则它们被调整到对应的指针类型。<span class="t-rev-inl t-since-cxx11"><span>允许<a href="parameter_pack.html" title="cpp/language/parameter pack">形参包</a>。</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>
</p><p>若函数抛出了未列于其异常说明的类型的异常，则调用函数 <span class="t-lc"><a href="../error/unexpected.html" title="cpp/error/unexpected">std::unexpected</a></span>。缺省的函数调用 <span class="t-lc"><a href="../error/terminate.html" title="cpp/error/terminate">std::terminate</a></span>，但它可以（通过 <span class="t-lc"><a href="../error/set_unexpected.html" title="cpp/error/set unexpected">std::set_unexpected</a></span>）替换为用户提供的函数，可能调用 <span class="t-lc"><a href="../error/terminate.html" title="cpp/error/terminate">std::terminate</a></span> 或抛出异常。若从 <span class="t-lc"><a href="../error/unexpected.html" title="cpp/error/unexpected">std::unexpected</a></span> 抛出的异常为异常说明所接受，则栈回溯照常持续。若它不被接受，但异常说明允许 <span class="t-lc"><a href="../error/bad_exception.html" title="cpp/error/bad exception">std::bad_exception</a></span>，则抛出 <span class="t-lc"><a href="../error/bad_exception.html" title="cpp/error/bad exception">std::bad_exception</a></span>。否则，调用 <span class="t-lc"><a href="../error/terminate.html" title="cpp/error/terminate">std::terminate</a></span>。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx17"><td>
<h3> <span class="mw-headline" id=".E6.BD.9C.E5.9C.A8.E5.BC.82.E5.B8.B8">潜在异常</span></h3>
<p>每个函数 <code>f</code>，函数指针 <code>pf</code>，与成员函数指针 <code>pmf</code> 都拥有一个“潜在异常集合”，它由可能抛出的类型构成。所有类型的集合指示可能抛出任何异常。此集合定义如下：
</p>
<div class="t-li1"><span class="t-li">1)</span> 若 <code>f</code>、<code>pf</code> 或 <code>pmf</code> 的声明使用 <code>throw()</code><span class="t-mark">(弃用)</span> 或 <a href="noexcept.html" title="cpp/language/noexcept">noexcept</a>，则集合为空。</div>
<div class="t-li1"><span class="t-li">2)</span> 否则，若 <code>f</code>、<code>pf</code> 或 <code>pmf</code> 使用动态异常说明<span class="t-mark">(弃用)</span>，则集合由列于该规定的所有类型组成</div>
<div class="t-li1"><span class="t-li">3)</span> 否则，集合是所有类型的集合</div>
<p>注意：对于隐式声明的特殊成员函数（构造函数、赋值运算符和析构函数），以及对于继承的构造函数，潜在异常的集合是它们会调用的所有函数的潜在异常集合的并集：非变体非静态数据成员、直接基类及适当场合的虚基类的构造函数/赋值运算符/析构函数（还包括默认实参表达式）
</p><p>每个表达式 <code>e</code> 都拥有一个<i>潜在异常集合</i>，它是 <code>e</code> 的全部直接子表达式（包含<a href="default_arguments.html" title="cpp/language/default arguments">默认实参表达式</a>）的潜在异常集合的并集，再与下列取决于 <code>e</code> 的形式的另一个集合合并：
</p>
<div class="t-li1"><span class="t-li">1)</span> 若 <code>e</code> 是一个函数调用表达式，且
<ul><li> 函数以标识表达式指名（或直接，或作为成员访问或成员指针访问表达式的一部分），则将所指名的函数的潜在异常集合添加到列表。
</li><li> 若函数以 noexcept 函数类型的表达式指名，或以指向 noexcept 函数的指针类型的表达式指名，则该集合为空
</li><li> 否则，该集合是所有类型的集合</li></ul></div>

<div class="t-li1"><span class="t-li">2)</span> 若 <code>e</code> 隐式调用某个函数（它是运算符表达式且该运算符被重载，是 <a href="new.html" title="cpp/language/new">new 表达式</a>且其分配函数被重载，或是完整表达式且调用了临时量的析构函数），则该集合是这个函数的集合。</div>
<div class="t-li1"><span class="t-li">3)</span> 若 <code>e</code> 是一个 <a href="throw.html" title="cpp/language/throw">throw 表达式</a>，则该集合是以其操作数所初始化的异常，或对于重抛出表达式（无操作数者）是所有异常的集合</div>
<div class="t-li1"><span class="t-li">4)</span> 若 <code>e</code> 是对多态类型引用的 <a href="dynamic_cast.html" title="cpp/language/dynamic cast">dynamic_cast</a>，则该集合由 <span class="t-lc"><a href="../types/bad_cast.html" title="cpp/types/bad cast">std::bad_cast</a></span> 组成</div>
<div class="t-li1"><span class="t-li">5)</span> 若 <code>e</code> 是应用到多态泛左值的 <a href="typeid.html" title="cpp/language/typeid">typeid</a>，则该集合由 <span class="t-lc"><a href="../types/bad_typeid.html" title="cpp/types/bad typeid">std::bad_typeid</a></span> 组成</div>
<div class="t-li1"><span class="t-li">6)</span> 若 <code>e</code> 是一个拥有非常量大小的 <a href="new.html" title="cpp/language/new">new 表达式</a>，则集合由 <span class="t-lc"><a href="../memory/new/bad_array_new_length.html" title="cpp/memory/new/bad array new length">std::bad_array_new_length</a></span> 组成</div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>  <span class="co1">// f() 的集合是“int”</span>
<span class="kw4">void</span> g<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>             <span class="co1">// g() 的集合是所有类型的集合</span>
<span class="kw1">struct</span> A <span class="br0">{</span> A<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>    <span class="co1">// “new A”的集合是所有类型的集合</span>
<span class="kw1">struct</span> B <span class="br0">{</span> B<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// “B()”的集合为空</span>
<span class="kw1">struct</span> D<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> D<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span> <span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// “new D”的集合是所有类型的集合</span></pre></div></div>
<p>所有隐式声明的成员函数（及继承的构造函数）都拥有异常说明，选择如下：
</p>
<ul><li> 若潜在异常为类型全集，则隐式异常说明为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span></span></span>。
</li><li> 否则，若潜在异常的集合非空，则隐式异常说明列出每个来自该集合的类型
</li><li> 否则，隐式异常说明为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span><span class="kw2">true</span><span class="br0">)</span></span></span> 且函数是“noexcept 函数”
</li></ul>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> A <span class="br0">{</span>
    A<span class="br0">(</span><span class="kw4">int</span> <span class="sy1">=</span> <span class="br0">(</span>A<span class="br0">(</span><span class="nu0">5</span><span class="br0">)</span>, <span class="nu0">0</span><span class="br0">)</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
    A<span class="br0">(</span><span class="kw4">const</span> A<span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    A<span class="br0">(</span>A<span class="sy3">&amp;&amp;</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    ~A<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span>X<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> B <span class="br0">{</span>
    B<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    B<span class="br0">(</span><span class="kw4">const</span> B<span class="sy3">&amp;</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span> <span class="co1">// 异常说明是“noexcept(true)”</span>
    B<span class="br0">(</span>B<span class="sy3">&amp;&amp;</span>, <span class="kw4">int</span> <span class="sy1">=</span> <span class="br0">(</span><span class="kw1">throw</span> Y<span class="br0">(</span><span class="br0">)</span>, <span class="nu0">0</span><span class="br0">)</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
    ~B<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span>Y<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">7</span><span class="sy4">;</span>
<span class="kw1">struct</span> D <span class="sy4">:</span> <span class="kw1">public</span> A, <span class="kw1">public</span> B <span class="br0">{</span>
    <span class="kw4">int</span> <span class="sy2">*</span> p <span class="sy1">=</span> new <span class="br0">(</span><a href="../memory/new/nothrow.html"><span class="kw699">std::<span class="me2">nothrow</span></span></a><span class="br0">)</span> <span class="kw4">int</span><span class="br0">[</span>n<span class="br0">]</span><span class="sy4">;</span>
    <span class="co1">// D 拥有下列隐式声明的成员：</span>
    <span class="co1">// D::D() throw(X, std::bad_array_new_length);</span>
    <span class="co1">// D::D(const D&amp;) noexcept(true);</span>
    <span class="co1">// D::D(D&amp;&amp;) throw(Y);</span>
    <span class="co1">// D::~D() throw(X, Y);</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;exception&gt;</span>
<span class="co2">#include &lt;cstdlib&gt;</span>
 
<span class="kw1">class</span> X <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> Y <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> Z <span class="sy4">:</span> <span class="kw1">public</span> X <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> W <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="kw1">throw</span><span class="br0">(</span>X, Y<span class="br0">)</span> 
<span class="br0">{</span>
    <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
    <span class="kw1">if</span> <span class="br0">(</span>n<span class="br0">)</span> <span class="kw1">throw</span> X<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
    <span class="kw1">if</span> <span class="br0">(</span>n<span class="br0">)</span> <span class="kw1">throw</span> Z<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 亦 OK</span>
    <span class="kw1">throw</span> W<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 将调用 std::unexpected()</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
  <a href="../error/set_unexpected.html"><span class="kw791">std::<span class="me2">set_unexpected</span></span></a><span class="br0">(</span><span class="br0">[</span><span class="br0">]</span><span class="br0">{</span>
      <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"That was unexpected"</span> <span class="sy1">&lt;&lt;</span> <a href="../io/manip/endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span> <span class="co1">// 需要冲洗</span>
      <a href="../utility/program/abort.html"><span class="kw966">std::<span class="me2">abort</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
  <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
  f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">That was unexpected</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<ul><li><a href="noexcept_spec.html" title="cpp/language/noexcept spec"><code>noexcept</code> 说明符</a>
</li></ul>

<!-- 
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Preprocessor generated node count: 5823/1000000
Post‐expand include size: 38390/2097152 bytes
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